examples of non-crystal based clocks in digital computing?
Hey All, I have one simple specific question, without a simple answer and general call for examples. I’m researching timing clocks used in general purpose digital computing. I’m starting to think that Ace/Pilot Ace by Alan Turing is the start of clock based general purpose computers. I’m starting to conclude the earlier computers were all basically clocked by the media holding the instructions. Is this correct? I’m currently looking for examples of general purpose computers that do not use crystal based clocks. Any thoughts appreciated. Ben
-----Original Message----- From: Ben Greenfield [mailto:ben@cogs.com] Sent: 13 March 2016 09:33 To: vcf-midatlantic <vcf-midatlantic@lists.vintagecomputerfederation.org> Subject: examples of non-crystal based clocks in digital computing?
Hey All,
I have one simple specific question, without a simple answer and general call for examples.
I’m researching timing clocks used in general purpose digital computing. I’m starting to think that Ace/Pilot Ace by Alan Turing is the start of clock based general purpose computers. I’m starting to conclude the earlier computers were all basically clocked by the media holding the instructions.
It depends on how you look at it. The Pilot Ace used mercury delay lines. The speed of propagation of waves in mercury is fixed. So for a given length of mercury, and a given number of bits to be stored, there is a fixed bit rate that’s required. So I would argue that for any machine using delay line store the clock cycle is fixed by the mechanical properties of the delay line and the word length. The Manchester SSEM (and I assume the Manchester MK1 as it was derived from the SSEM) has a master clock that can have its frequency changed by a knob. In fact the clock speed was tweaked several times early in the development cycle. So machines that use Storage Tubes for displays can be built as true variable speed machines. Even the Pegasus which derives its clock from the drum has a cheat. It uses the tracks on the drum in pairs so the data can be clocked off at twice the bit rate of the drum. The real break through came with Computers like the Atlas (and I assume Stretch) where you start to get asynchronous processing and the various parts of the machine are no longer all clocked together...
Is this correct?
I’m currently looking for examples of general purpose computers that do not use crystal based clocks.
Any thoughts appreciated.
Ben
Dave
The Scelbi 8H and 8B do not use crystals for system clocks which is why they need military spec parts in the timing circuits or they drift as the temperature of the system changes. corey cohen uǝɥoɔ ʎǝɹoɔ
On Mar 13, 2016, at 5:32 AM, Ben Greenfield <ben@cogs.com> wrote:
Hey All,
I have one simple specific question, without a simple answer and general call for examples.
I’m researching timing clocks used in general purpose digital computing. I’m starting to think that Ace/Pilot Ace by Alan Turing is the start of clock based general purpose computers. I’m starting to conclude the earlier computers were all basically clocked by the media holding the instructions.
Is this correct?
I’m currently looking for examples of general purpose computers that do not use crystal based clocks.
Any thoughts appreciated.
Ben
The Scelbi 8H and 8B do not use crystals for system clocks which is why they need military spec parts in the timing circuits or they drift as the temperature of the system changes.
Many early hobbyist computers didn't -- it was common with 8008 and 6502 homebrew designs to just use a RC oscillator. Several of Ohio Scientific's 6502-based systems used RC oscillators (the 400 board used a 555 for the more precise task of ACIA clock!), and the John Bell Engineering 6502 single-board embedded computer also used a RC oscillator, with a note on adding a crystal clock if you need stable timing. The Intel 8085 can use a RC (or LC) oscillator, but I don't think I've ever seen an example of that, probably because crystals had become cheap enough for hobbyists and even cost-reduced products by that point. Thanks, Jonathan
On 03/13/2016 05:32 AM, Ben Greenfield wrote:
I have one simple specific question, without a simple answer and general call for examples.
I’m researching timing clocks used in general purpose digital computing. I’m starting to think that Ace/Pilot Ace by Alan Turing is the start of clock based general purpose computers. I’m starting to conclude the earlier computers were all basically clocked by the media holding the instructions.
Is this correct?
I’m currently looking for examples of general purpose computers that do not use crystal based clocks.
Any thoughts appreciated.
I don't think this is really what you're looking for, but since it popped into my head I'd mention it just in case. The built-in console port on the PDP-11/05 and 11/10 processor board set uses an RC oscillator as a baud rate generator. It's very common in the modern microcontroller space. The SiLabs EFM32 ARM family has built-in RC clock generators, in particular, as do many others. The Green Arrays GA144 Forth array processor, positioned as a general-purpose microcontroller, takes it a step further with an asynchronous, i.e. non-clocked, design. -Dave -- Dave McGuire, AK4HZ New Kensington, PA
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